The present invention relates to the application of sizing to cellulose fibers and to a sized cellulose fiber product.
Sizing of cellulose fibers is known. In one conventional approach, an aqueous emulsion of sizing is added, at the wet end of a paper making process, in dilute form to the entire pulp furnish being used to make paper. This approach results in a loss of sizing material as some of the sizing material is discarded with the "white water" resulting from this process. Also, sizing is introduced into the paper making equipment and paper making wire. As another prior art example, an article entitled Chemically Modified Fiber as a Novel Sizing Material, by M. K. Gupta, published in Tappi, The Journal of the Technical Association of the Pulp and Paper Industry, Volume 63, No. 3, published March, 1980, describes the sizing of cellulose fiber with Aquapel water emulsion, a sizing material from Hercules, Inc. Aquapel is a water emulsion of alkyl ketene dimer. This article mentions that only a small portion of the furnish needs to be treated with Aquapel water emulsion and also that the treated fibers may be prepared at a convenient time and simply blended into the paper furnish. As described in this article, the first step in the process of producing these sized fibers is to saturate pulp with an Aquapel water emulsion. Treatment with a 4 percent Aquapel water emulsion for a 0.2 percent retention in the final sheet is mentioned. However, drying of these treated fibers is required before they can be used to fix the sizing chemical on the paper. This approach substantially eliminates sizing from white water and from introduction into the paper making equipment because the sizing is retained on the fibers. Aquapel water emulsion can deteriorate when exposed to hot or cold climates and when exposed process conditions if simply added to the wet end of a paper making process. The process as described in thie article advantageously overcomes these problems because fiber can be sized in advance, before the shelf life of the Aquapel water emulsion is affected by environmental conditions, with the sized fiber subsequently being blended with other fiber to make paper. The use of sized fibers eliminates the need to handle and mix sizing chemicals of the wet end of a paper making process. These advantages are also present in the present invention without the disadvantage of having to dry the sized fibers prior to use under the approach of this article.
In addition, known aqueous solutions of Aquapel used in sizing fibers started with a relatively expensive raw material, namely a cationized Aquapel emulsion.
U.S. Pat. No. 3,212,961 of Weisgerber relates to the pretreatment of paper pulp with ketene dimer to improve sizability. Column one of this patent mentions that the pretreatment can be carried out in any manner which will cause the pretreating material, for example the aqueous ketene dimer emulsion, to become permanently anchored or attached to the pulp fibers. Spraying of the emulsion on the fibers is mentioned with the fibers then being dried. The Weisgerber patent does not describe how the spraying of aqueous ketene dimer emulsion is accomplished other than at column 5 where spraying of sheets with aqueous ketene dimer emulsion is mentioned. The addition of aqueous ketene dimer emulsion to an aqueous pulp suspension is also mentioned. Following pretreatment, the fibers are processed into sized paper with sizing material being added internally prior to sheet formation or externally to the sheet after it is formed. Following pretreatment, sizing agents, such as alkyl ketene dimer, are used. The sizing is described as being carried out internally by adding the sizing agent, preferably in the form of an aqueous emulsion or dispersion to the beater of a paper making system, or by surface application, as by tub-sizing, spray application or the like.
Although prior art approaches are known, a need exists for an improved method of sizing cellulose fibers and to an improved sized cellulose product.